The electrical conversion system of wind turbines greatly affects the loads of such mechanical parts as the gear box, shaft and blades in wind turbines. The application of variable speed contributes to the reduction of mechanical stress in these components. A number of different electrical conversion systems for application in variable speed turbines can be distinguished, all with different properties with respect to efficiency, costs, reliability and so on. Recent developments in power electronics and machine technology have afforded the possibility of applying new types of electrical conversion systems in variable speed wind turbines.
The results of the project indicate that a small-size variable speed wind turbine with VRG has an electric efficiency similar to that of systems with synchronous or induction machines and has good controllability. Variable speed operation was successful between 1000 and 1500 rpm, which covered the major part of the power range (2 - 18 kWe). The overall electric efficiency ranges from 80% at 2 kWe to 90% at 18 KWe, while the machine efficiency varies between 82% and 92%; similarly rated synchronous and induction machines have an efficiency of <90% at rated load.
Tracking to changing wind speed proved to be sufficiently fast for the realisation of expected variable speed benefits under real turbulent field conditions. Below 1000 rpm high acoustic noise levels were observed. These are probably due to the mechanical design of the reluctance machine for constant speed operation at 1500 rpm. Equipment cost is not reduced when reluctance machines are operated at constant rotor speed. Hence a constant speed wind turbine with reluctance machine is not a viable option.
The main objective of this project is the development of an electrical conversion system consisting of a Variable Reluctance Generator (further referred to as VRG) and a Power Electronic Converter (further refered to as PEC) for variable speed wind turbine applications. This type of generator seems suited to be used in a so called "direct drive", (i.e. a drive train without gearbox). In this application the generator is more robust and is cheaper than other types of genrators, while the power electronics is relatively simple. The ommission of a gearbox may contribute to the reliability of windturbines.
The project aims at development of an optimised integrated design of the VRG and the PEC with respect to efficiency, including overall control system.
The system will be realized and tested in the windturbine simulator of ECN.
It is expected that the system will be applied in a 20 kW windturbine. The project may contribute to the development of direct drives for application in variable speed windturbines in the 0.5 MW range.
Funding SchemeCSC - Cost-sharing contracts
SN14 6NO Chippenham